Launches program as a daemon and keeps it running. Adds log and pid file support to the program.

daemon-launcher.sh

#!/bin/bash
#
# Daemoniser:  starts a program as a daemon and relaunches it if it exits. Adds a pidfile and
# logfile capabilities.
#
# dsimmons@squiz.co.uk
# 2011-10-28
#

usage()
{
	echo "Usage: $0 [--pidfile=<path>] [--logfile=<path>] [--user=<user>] <program> [args]" >&2
}

log()
{
	fd=${2-1}
	echo "[$(date +%c) - ${0##*/}]: $*" >&$fd
}

signal_handler()
{
	log "Received signal, killing $daemon_bin pid $daemon_pid"
	kill $daemon_pid
}

while [ "$1" != "${1##-}" ]; do
	case $1 in
		--no-detach)
			foreground=true
			shift
			;;

		--pidfile=?*)
			pidfile=${1#--pidfile=}
			shift
			;;

		--logfile=?*)
			logfile=${1#--logfile=}
			shift
			;;

		--user=?*)
			user=${1#--user=}
			shift
			;;
		*)
			usage
			exit 99
			;;
	esac
done

daemon_bin="$*"

if [ -z "$daemon_bin" ]; then
	usage
	exit 99
fi

# Spawn daemon process and exit
if [ ! $foreground ]; then
	args="--no-detach"
	[ -n "$logfile" ] && args="$args --logfile=$logfile"
	[ -n "$pidfile" ] && args="$args --pidfile=$pidfile"
	$0 $args $* &
	exit
fi

# Direct all output to logfile if one has been specified
if [ -n "$logfile" ]; then
	exec 3>>$logfile
	logfd=3
else
	logfd=-
fi

# Close stdin and redirect or close other fds
exec <&-
exec 1>&$logfd
exec 2>&$logfd

# Set signal handler to clean up the child program on exit (or HUP)
trap signal_handler SIGHUP EXIT

# Write pid if a pidfile has been specified
[ -n "$pidfile" ] && echo $$>$pidfile

while true; do

	if [ -z "$user" ]; then

		log "Launching $daemon_bin"
		$daemon_bin &
		daemon_pid=$!

	else

		log "Launching $daemon_bin as user $user"
		su $user -c "$daemon_bin" &
		daemon_pid=$!

	fi

	log "PID is $daemon_pid"
	wait $daemon_pid

	log "$daemon_bin exited"
	sleep 2

done